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Tikvah Hayes



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    P2.03 - Biology (ID 162)

    • Event: WCLC 2019
    • Type: Poster Viewing in the Exhibit Hall
    • Track: Biology
    • Presentations: 1
    • Moderators:
    • Coordinates: 9/09/2019, 10:15 - 18:15, Exhibit Hall
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      P2.03-39 - Systematic Evaluation of EGFR Variant Biology in Cancer (ID 2572)

      10:15 - 18:15  |  Presenting Author(s): Tikvah Hayes

      • Abstract

      Background

      Lung cancer is the leading cause of cancer related deaths world-wide, with non-small cell lung cancer (NSCLC) accounting for a majority of all cases. Approximately 14% of adenocarcinomas, a NSCLC subtype, are characterized by activating mutations in the epidermal growth factor receptor, EGFR. In NSCLC, there are several well-established hotspot mutations in EGFR, such as in-frame deletions in exon 19 and point mutations at residue L858, that have demonstrated dramatic responses to molecularly targeted therapies in subsets of patients. Beyond hotspot mutations, subsets of patients can present with rare EGFR variants at residues G719, L861, or S768, all of which are known to be oncogenic drivers. However, a subset (~5%) of observed EGFR variants remain functionally uncharacterized. Given the increase in targeted panel sequencing of cancer patients, it is feasible that additional EGFR variants will be revealed beyond those already functionally annotated. Additionally, pre-clinical and clinical investigations have revealed that EGFR variants, rare or not, can have differential sensitivity to EGFR TKIs (tyrosine kinase inhibitor), however, the mechanism for this differential sensitivity remains to be elucidated. If we could systematically assess whether an EGFR variant is a possible driver and determine its TKI sensitivity profile, this could pave the way towards enhanced patient care by providing a catalogue of treatment strategies for specific EGFR variants.

      Method

      To systematically evaluate all possible EGFR variants, we employed a high throughput forward genetic screening approach. To generate all possible EGFR variants, we used a saturation mutagenesis strategy, which entailed substituting each amino acid for all other possible amino acids including stop codons, generating a library of approximately 25,000 EGFR variants. We expressed our pooled library in two distinct lung cancer models and assessed the ability of each EGFR variant to grow compared to EGFR WT in the presence of inhibitors using changes to population doublings as a readout for variant functionality.

      Result

      Our screens revealed functional information for somatic mutations observed in patients that previously were uncharacterized. Firstly, in both screens, we observed variant enrichment in the kinase domain, which was expected and gives us confidence that our screens have yielded relevant EGFR variant biology. Furthermore, in our oncogenesis screen, we unexpectedly identified variant enrichment in specific EGFR extracellular domains. Conversely, in the second screen, which measured EGFR activity and insensitivity to erlotinib, we observed a distinct variant enrichment pattern in both the EGFR extracellular domain and the transmembrane domain.

      Conclusion

      Our strategy is a powerful tool to uncover novel functional information for variants of unknown significance (VUS). Together, our screening results give a comprehensive understanding of the EGFR variant landscape, which has implications for both EGFR biology and patient treatment strategies.